* Taliban have vowed to use 'full force' to disrupt April 5 election (Updates with Kandahar attack, nationalities of Kabul victims)

By Jessica Donati and Hamid Shalizi

KABUL, March 21 (Reuters) - A Taliban assault on the restaurant of a luxury hotel considered one of the safest places in Kabul and frequented by foreigners and Afghan officials has added to a tide of violence sweeping Afghanistan two weeks before a presidential election.

Taliban gunmen smuggled tiny pistols past the Serena hotel's heavy security cordon and waited for the restaurant to fill up for an Afghan New Year dinner before emerging to shoot diners point-blank. Three children between two and five were found with bullets in their heads. Four of the nine dead were foreigners.

Hours later, a bomb attack in the southerly Kandahar province wounded the deputy governor and left his chief of staff in critical condition.

The Islamist movement has ordered its fighters to use "full force" to disrupt the vote and threatened to kill anyone who participates in what it calls a Western-backed sham.

This week alone, seven or eight suicide bombers killed at least 11 people in the eastern city of Jalalabad, while 18 were killed by a bomb in a marketplace in northern Afghanistan.

The April 5 vote is intended to mark the first democratic transfer of power in Afghanistan's history. It will be a pointer the prospects for stability as the NATO force that has been reinforcing security since the Taliban were driven from power in 2001 prepares to withdraw most of its troops this year.

The hotel attack started around 6 p.m. on Thursday when four attackers managed to get past the dozens of armed guards patrolling the perimeter as well as metal detectors and body searches, possibly concealing their guns in their socks.

Three hours later, they emerged to begin their rampage, killing four foreigners from Canada, Paraguay and Bangladesh, acccording to Interior Ministry spokesman Sediq Sediqqi.

The dead Afghans included the popular journalist Sardar Ahmad of Agence France-Presse, his wife and his two daughters, celebrating the Afghan New Year.

BASEMENT SAFE ROOM

Afghan special forces fought the gunmen for hours as terrified guests barricaded themselves in darkened rooms, listening to gunfire and the sound of running. Around 100 guests fled into a basement safe room, where they had to struggle with choking smoke from a fire in the kitchen above.

Although six people were killed in an attack on the Serena Hotel in 2008, its heavy security made it one of few places in Kabul where foreign officials were still permitted to dine, after 21 people including three U.N. staff and a senior IMF official were killed in a Lebanese restaurant in January.

As shots rang out and diners dived under tables, one witness said Sardar had motioned for a foreign man desperately seeking a hiding place to take cover under a table with him and his children.

As two gunmen walked towards the group, Sardar spoke to them in a local language and the gunmen turned away and started shooting in a different direction until they ran out of bullets.

As they reloaded, the foreigner ran into the kitchen, where staff were guiding customers toward the safe room. But Sardar, his wife and two daughters were killed. Their young son was shot in the head, chest and leg, and was in critical condition.

All the Taliban gunmen were eventually shot dead, Sediqqi said. The bodies were dragged through the hotel lobby, leaving long smears of blood, a witness said. Like the others, he asked not to be identified because he was not authorised to speak to the media.

Friday's attack in Kandahar killed at least one person and wounded nine, leaving the governor's chief of staff fighting for his life in a military hospital, officials said.

"The doctor says that he is alive, he's in a coma, but will be okay," said Tawab Ghorzang, a spokesman for Afghanistan's governance agency. (Additional reporting by Katharine Houreld and Mirwais Harooni; Editing by Maria Golovnina and Andrew Roche, Simon Cameron-Moore and Michael Perry and Miral Fahmy)